Alkaline digestion of cottonseed hulls



Patented Jan. 2, 1951 f 2.536.046. ALKALINE DIGESTION or co'r'ronsnnn nuLLs i Jefferson L. Eskridge, Long Island City, N. Y.

No Drawing. Application July 17, 1945,

* Serial No. 605,640

6 Claims. (Cl-92 13) casecontain s matter continued from my copending application Serial No. 324,623, dated March; 18,. 1940, and my copending application 398,411, filed June .17, 1941, both of which are, now abandoned. 4 i

This invention relates to an improved process for recoveringcomparatively high grade alpha cellulose from a comparatively low grade and cheap cellulose-containing, material, namely the cotton seed hulls which stillcarry some fuzz of fibre, not removable in :the usual ginning and ,tdelintering operations. These hulls are utilized for obtaining a fairly high grade cellulose and with a fairly high yield. In practice the yield and quality of cellulose which are obtained when hulls are used are not so high as-those obtained from linters or hull fibres (covered in a concurnew and novel characteristics, particularly alpha cellulose pulp having a low copper number and a low ash content and of a quality. suitable for chemical treatment (e. g. nitration or acetylatidn) Y l In the process, the cotton seed hull," as treated herein, contains a substantial amount of adhering fuzz of short fibres. The cotton seed is usually first ginned to remove the staple. and

"then delintered to produce linters. The' seed coat or hull still carrying fuzz is then broken and the hull (carrying this fuzz) is separatedfrom the kernel. It is in this condition that I use the hulls in the'process of the present case. It is the fuzz on thehulls which contain themain amount (at least) of the recoverable cellulose, since the seed coat itself is mostly all dissolved during the cooking.

Igive the following examples as illustrative, the invention not being restricted to the details thereof.

Example 1 Cotton seed as above described, constitute the raw material to1be treated. The procedure may be as follows: The chemical requirements per ton of hulls are given below:

360 lbs. of sodium hydroxide (=18% based on the hulls treated) W lbs. of ammonium hydroxide (26 Be. 22.5 lbs. of potassiumcarbonate 7.5 lbs. of ammonium oxalate 10,000 lbs. of distilled water i i In a particular experimentoi' digesting the cotton seed hulls, 6.6 lbs. of 'hulls containing 9.5% moisture (i. e. air-dry) were charged into a stainless steel rotary autoclave. Two-thirds of the total water required by'the" above formula,

solution) was added-to the bulls in thedigester on the night before the cook in order to allow the hulls to soak over nightinwater before the digesting operation was started. The chemicals in their proper proportions were dissolved separately in the rest of the water, mixed together and added to the digester already containing hulls and water. The digester was sealed and heat was applied to the digester. The pressure in the digester was brought up to 110 lbs. per square inch. in about twenty minutes. It was thereafter maintained at this point for three hourswithout any gas relief. During this time the temperature in the digester varied between 170 and 172 C. i

It will be seen that the cooking liquor, in this example, per ton of cotton seed hulls to be cooked, amounts to about 10 405 lbs. and contains about 3.46% of caustic soda and about 3.89% of total chemicals. In the cooking of cotton seed hulls,

as will be seen, by comparing these figures with the figures in the specific example of my concurrent application Ser. No. 605,639, .the digesting cotton seed hull fibre, a more concentrated liquid is here used, in order to dissolve up nearly all of the hull substance. b

After the digester was blown the pulp was dumped from the digester on to a fine muslin cloth. Then approximately one-fourth ofthe pulp was placed in a pail and was diluted with hot tap water and thereafter poured over an inclined wire screen to separate the finer fibres and any other very fine material. The separating arrangement consisted of a by mesh Fourdrinier wire stretched over a wooden frame and inclined at about a. 50 degree angle to the horizontal. The wire was seated in a bottomless wooden box so arranged that the fine fibres passing through the wire were collected in a fine muslin cloth directly below' the wire, while the coarser fibres could be washed down the incline into another fine muslin cloth. The pulp retamed on the wire was picked up and diluted in a pail and again poured over the wire. This operation' was repeated until no more fines passed through. The fines were not considered acceptable for bleaching, but were dried and weighed separately. The weight of the fines was included in the total yield of unbleached pulp. After the foregoing procedure was carried out, the remaining pulp was left standing over night before the final washing step, but this is optional. For final washing the accepted pulp was placed in a beater and circulated for thirty minutes, using a balanced bedplate.

At the conclusion of the beating period, the pulp was removed from the beater and washed down the inclined screen to remove any additional fines which the beating might have dislodged. The pulp retained on the wire after the second washing operation was considered satisfactory forv bleaching.

A portion of this accepted pulp" was then bleached using hypcchlorite solution containing (based on the accepted pulp) 7.5% of available I chlorine.

Test figures for the foregoing operations are as follows:

Evaluation Data Per cent Total unbleached yield 47.9 Accepted pulp yield (fines removed) 22.3 Bleaching loss (based on acceptable pulp) 4.6 Alpha-cellulose in unbleached pulp 89.6 Alpha-cellulose in bleached pulp 86.8

It will be noted that there was degradation of the pulp from 89.6 to 86.8% during the bleaching step which was carried out in the absence of the inhibiting ingredients-viz. ammonium hydroxide potassium carbonate and ammonium oxalate --in the bleaching solution.

Example 2 1 ton of air-dry cotton seed hulls (after soaking in water for 14 hours) were digested for about 2 hours in a solution made up as follows:

20,000 lbs. water 480 lbs. NaOH 20 lbs. NHQOH of 26 B. 30 lbs. KzCOs 10 lbs. ammonium oxalate (cryst.)

The digestion was at 300 to 350 F. 149 to 177 C.) under pressure. During this treatment most of the hull proper (horny seed coat) was dissolved.

The pulp was washed, screened as above to remove fines, and dried. Yield of cellulose pulp was good. It will be noted that here, the ratio of water to cotton seed hull was 1021, and the NaOH was equal to 24% of the weight of the cot- 4 this account that the percentage of NaOH (based on' the hulls) is large.

Example 3 Three ounces grams) of air-dry cotton seed hulls (2 years old) were placed in a steam Jacketed autoclave with a digesting solution which comprised 64 ounces ,5 gal. or about 1.9 liters) of water in which had been dissolved 17 grams of caustic soda, 0.08 gram of 26 B. ammonia water, 0.12 gram of potassium carbonate and 0.04 gram 01' ammonium oxalate. The autoclave was sealed and steam under pressure admitted to the jacket. During cooking, the steam pressure varied from to lbs. However, the temperature within the digester was maintained at a mean temperature of 335 degrees F. (i. e. about 170 C.) for a period of three hours. At the conclusion of this cooking period the autoclave was vented to gradually reduce the pressure within the same. It was noticed that there was an absence of ammonia in the steam and other gases which escaped from the autoclave when it was vented. The pulp was removed from the autoclave and carefully washed and then dried. When thoroughly dried it was carefully weighed and a yield determination made. It was found that the yield was slightly over 50% (based on the cotton seed hulls treated).

While I have given above the ingredients and relative proportions of ingredients to obtain good yields of alpha cellulose pulp with desirable characteristics from cotton seed hulls, it will be apparent to those skilled in the art that the proportions andamounts of chemicals to be used may in some instances be varied, depending upon the kind, quality, condition and state or source of supply of the raw cotton seed hulls available. In practice and based upon many tests and experiments which I have made, the proportion and ingredients for digesting and cooking cotton seed hull may vary as follows and yet afford the most advantageous results in the described process.

When cotton hulls are digested, the proportions and amounts of the ingredientsper ton of bulls may be varied as follows, while affording very advantageous results in the described process, both as to yield and quality of cellulose.

- Pounds per ton NaOH (alone or with carbonate),

16 to 24% 330 to 480 Water, about 500% to 1200% 10,000 to 24,000

NH40H (26 Be), H of 1% t0 1% 13% b0 20 KzCOa (98%), 1 to 20% to 30 (NH4):C:O4 (crys. 0.1).), H% to v By the foregoing process, cotton seed hulls can be processed so as to obtain relatively high yields of cellulose pulp. The pulp also has a high alpha cellulose content. By carrying out the digesting operation in the presence of ammonium hydroxide, potassium carbonate and ammonium oxalate, degrading of the cellulose which tends to take place under the action of the relatively strong alkaline digesting solution is restrained. It is not intended to imply by the inclusion inthe summary table above, that the ammonium hydroxide must be added as 26 B." ammonia water (i. e., containing 28% NH: in solution), but that the amount of ammonia solution used is equivalent to the stated amount of 26 ammonia. Similarly the reference to 98% calcined in referring to the potassium carbonate, and the refrenc a .a y m? n, r i r ns t the mm nium oxalate, are for showing 'thatfthe amounts ounds) of these isubstances are calculated on thesebas'es. Thealpha cellulose obtained also ha the desirablecharacteristics which are shown 6. a a a a a p a V H approximately 16.5 to 24%, based on the air-dry by test data figures.

In the aboveexamples, I have statedilpreferred temperatures, pressures and tlines'of treatment, which have been found .toiibe satisfactory. It is ammimiumhydroxide calculated ses, B. and.

1 about three arts or potassiumfcarbonate, the amount of said inhibitor being from about onetenth to? about one-sixth. of the amount of said Catistlfisbda, thefamount'of caustic sodmbeins weight of tbesaid cotton seed hullaand continui g said ,"digestion until the said pieces of seed coat] are substantially all separated irom the not desired, however, to limit the invention to l subject to variation. In assesses, I prefer to maintain thetemperatureduringthe cooking, at

about 160 to 170 0., although the temperature mam-fluctuate over ,a somewhat wider range.

these details, since it beapnarent to those V grammar with the art, thatthese featuresjare cottonseed hullilbres and disintegrated.

A process "or obtaining amna cellulose from ,co'tton seed hulls carrying cotton seed hull fibre rigidlyattached thereto, which comprises digesting, the premoistened hulls under pressure and ate. temperature of about 171. C. in a digesting solution containing the following ingredients ex- C. have given good results. The time during which these temperatures are maintained is also variable; times 2, 2% and 3 hours are given in the examples, as suitable. But it will be understood that the cooking is to be continued until the cellulose fibre is sufficiently loosened, and until the hard seed coat is dissolved or disintegrated. This is generally a few hours. The pressures obviously willbe dependent on the temperature of the cooking operation, since the pressure is developed by the boiling of the solution or liquor in the digester and the liberation of vapors therefrom- In the examples, I have mentioned, by way of example, pressures of 52 lbs. to 135 lbs., per square inch, as being suitable. Generally, with a given material (seed hulls and solution) to be digested, high pressure will be produced by high temperature, and vice versa.

Cotton seed hull, in air-dry condition may contain about 7 to 10% of moisture. These figures will vary somewhat depending on the atmospheric conditions during the drying and storage of the materials in question.

Operating in accordance with Example 1 above, I have made alpha cellulose of 95% purity, having very satisfactory properties for use in making such products as nitrocellulose '(for explosives).

The cotton seed hulls carries a substantial amount of short flbered cotton fuzz attached to pieces of the hard, horny seed coat, the latter component amounting to roughly one half (50%) of the said material, and horny seed coat as is well known, does not contain but a very small percentage of alpha cellulose. This "seed coat or actual hull of the seed has to be substantially pieces of the seed coat itself, which process comprises first soaking said material in water for at least several hours, then digesting such hulls in a closed pressure tight digester, under about 52 lbs. to about 135 lbs. pressure and at approximately 149 to 177 C., in an aqueous solution containing from .34% to 3.46% of caustic soda as, its main chemically active dissolved constituent, together with an inhibitor of degrading of the cellulose, which inhibitor consists essentially of one pressed in pounds ton of air-dry "hulls:

.360. pound of sodium hydroxide .15 pounds of ammonium hydroxide (26 22.5 pounds potassium carbonate 7.5 pounds ammonium oxalate 10,000 pounds water and continuing such digestion for a period of about 3 hours and until the seed coat component is substantially all dissolved.

3. A process of obtaining alpha cellulose from cotton seed hulls carrying cotton seed hull fibre rigidly attached thereto, which comprises digesting the premoistened hulls under super-atmospheric pressure, and at a temperature of about 149 to 177 C. in a digesting solution containing the following ingredients expressed in pounds per ton of air-dry hulls:

480 pounds of sodium hydroxide 20 pounds of ammonium hydroxide (26 Be.) 30 pounds potassium carbonate 10 pounds ammonium oxalate 20,000 pounds water 360 to 480 pounds of sodium hydroxide About 15 to about 20 pounds of ammonium hydroxide (26 B.)

About 22.5 to about 30 pounds of potassium carbonate About 7.5 to about 10 pounds ammonium oxalate About 10,000 to about 20,000 pounds water in which digesting solution the sodium hydroxide content amounts to between 2.34% and 3.46% and the sodium hydroxide is between 6 and 10 times the combined amounts of ammonium oxalate, 26 B. ammonia water and potassium carbonate, and continuing such digestion for a period of about 2 hours and until the seed coat component is substantially all dissolved.

5. In the art of digesting cotton seed hulls carrying a fuzz of cotton fibres rigidly attached to broken pieces of the seed coat itself, in caustic soda lye, of about 2.34% to about 3.46% concentration. under a superatmospheric pressure of about 52 pounds to about 135 pounds per square inch, and at approximately the boiling point of part of ammonium oxalate, about two parts of the said lye under the existing pressure. until said pieces 01' seed coat become substantially all disintegrated, the herein described improvement which consists in adding to said lye an inhibitor to inhibit the degradation of alpha cellulose present in said iuzz, which inhibitor contains about 1 5 part ammonium oxalate, about 2' parts of ammonia calculated as 26 B6. ammonia solution and about 3 parts of potassium carbonate, one part of said inhibitor being added to each 6 to 10 parts of caustic soda in said lye.

6. As a new composition of matter, a digestive solution which is a solution containing as its essential constituents, dissolved in water,

- Parts Ammonium oxalate Ammonium hydroxide, calculated as 26 31%.,

about 2 Potassium carbonate, about 3 Caustic soda, about 48 8 the percentage 0! caustiosoda in sueh'solution belns between about 2.34 and about 3.46.

JEFFERSON L. ESKRIDGE.

REFERENCES crr The following references are of record in the file of this patent:

UNITED STATES PATENTS m Number Name Date 1,842,649 Bassett Jan. 26, 1932 1,998,344 Thomas Apr. 16, 1935 FOREIGN PATENTS Number Country Date 347,444 Great Britain Apr. 30, 1931 

1. A PROCESS OF MAKING CELLULOSE OF HIGH ALPHA CONTENT FROM COTTON SEED HULLS CARRYING A FUZZ OF COTTON SEED HULL FIBERS RIGIDLY ATTACHED TO BROKEN PIECES OF THE SEED COAT ITSELF, WHICH PROCESS COMPRISES FIRST SOAKING SAID MATERIAL IN WATER FOR AT LEAST SEVERAL HOURS, THEN DIGESTING SUCH HULLS IN A CLOSED PRESSURE TIGHT DIGESTER, UNDER ABOUT 52 LBS. TO ABOUT 135 LBS. PRESSURE AND AT APPROXIMATLEY 149* TO 177* C., IN AN AQUEOUS SOLUTION CONTAINING FROM 2.34% TO 3.46% OF CAUSTIC SODA AS ITS MAIN CHEMICALLY ACTIVE DISSOLVED CONSTITUENT, TOGETHER WITH INHIBITOR OF DEGRADING OF THE CELLULOSE, WHICH INHIBITOR CONSISTS ESSENTIALLY OF ONE PART OF AMMONIUM OXALATE, ABOUT TWO PARTS OF AMMONIUM HYDROXIDE CALCULATED AS 26* BE. AND ABOUT THREE PARTS OF POTASSIUM CARBONATE, THE AMOUNT OF SAID INHIBITOR BEING FROM ABOUT ONETENTH TO ABOUT ONE-SIXTH OF THE AMOUNT OF SAID CAUSTIC SODA, THE AMOUNT OF CAUSTIC SODA BEING APPROXIMATELY 16.5 TO 24%, BASED ON THE AIR-DRY WEIGHT OF THE SAID COTTON SEED HULLS, AND CONTINUING SAID DIGESTION UNTIL THE SAID PIECES OF SEED COAT ARE SUBSTANTIALLY ALL SEPARATED FROM THE COTTON SEED HULL FIBRES AND DISINTEGRATED. 